/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.querydsl.lucene3;

import com.mysema.commons.lang.CloseableIterator;
import com.querydsl.core.QueryException;
import java.io.IOException;
import java.util.function.Function;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.FieldSelector;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.ScoreDoc;
import org.jetbrains.annotations.Nullable;

/**
 * {@code ResultIterator} is a {@link CloseableIterator} implementation for Lucene query results
 *
 * @author tiwe
 * @param <T>
 */
public final class ResultIterator<T> implements CloseableIterator<T> {

  private final ScoreDoc[] scoreDocs;

  private int cursor;

  private final IndexSearcher searcher;

  @Nullable private final FieldSelector fieldSelector;

  private final Function<Document, T> transformer;

  public ResultIterator(
      ScoreDoc[] scoreDocs,
      int offset,
      IndexSearcher searcher,
      @Nullable FieldSelector fieldSelector,
      Function<Document, T> transformer) {
    this.scoreDocs = scoreDocs.clone();
    this.cursor = offset;
    this.searcher = searcher;
    this.fieldSelector = fieldSelector;
    this.transformer = transformer;
  }

  @Override
  public boolean hasNext() {
    return cursor != scoreDocs.length;
  }

  @Override
  public T next() {
    try {
      Document document;
      if (fieldSelector != null) {
        document = searcher.doc(scoreDocs[cursor++].doc, fieldSelector);
      } else {
        document = searcher.doc(scoreDocs[cursor++].doc);
      }
      return transformer.apply(document);
    } catch (IOException e) {
      throw new QueryException(e);
    }
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }

  @Override
  public void close() {}
}
